jp6b04978_si_001.pdf (2.86 MB)
Laccase Redox Potentials: pH Dependence and Mutants, a QM/MM Study
journal contribution
posted on 2016-08-17, 00:00 authored by Jan P. Götze, Michael BühlWe have studied the T. versicolor laccase T1 site
redox potential (RP) at the M06/6-311++G**/SDD(Cu) level of theory,
employing QM/MM-optimized geometries (RI-BP86/def2-SVP/def2-TZVP(Cu):CHARMM)
of the whole protein system with electronic embedding. The oxidation
state of the trinuclear cluster was found to affect the T1 site RP
by about 0.2–0.3 V, depending on the protein protonation state.
The computed laccase RP can be drastically lowered upon introduction
of a protonation state corresponding to a neutral environment, by
up to −1.37 V, which is likely an overestimation of the effect
in vivo. The gradual change of the protonation state by single points
without optimization or equilibration results in a change that is
even larger, namely up to about −2.6 V. Thus, the preferred
protein conformation supports a high redox potential, compensating
for the RP-lowering effect of surface charges. The predicted change
in RP on going to the F463M mutant, ca. −0.1 V, is consistent
with observations for a related laccase. Based on our results, we
also propose and test a D206N mutant but find it to be locked in a
conformation with slightly lower RP.